Certified GKH Gardening Expert
Depending on your circumstances (container or garden plant), here is an article or two that you may find helpful: https://www.gardeningknowhow.com/ornamental/vines/passion-flower/passion-flower-winter-care.htm
As to your question regarding hollow fruits...this is oftentimes a result of the species (of which there are many). Some species only produce hollow fruits while others produce fruit with edible seeds and some pulp inside. Apparently, you have one of the hollow-producing fruit varieties.